net: fix a compile error when SOCK_REFCNT_DEBUG is enabled

When SOCK_REFCNT_DEBUG is enabled, below build error is met:

kernel/sysctl_binary.o: In function `sk_refcnt_debug_release':
include/net/sock.h:1025: multiple definition of `sk_refcnt_debug_release'
kernel/sysctl.o:include/net/sock.h:1025: first defined here
kernel/audit.o: In function `sk_refcnt_debug_release':
include/net/sock.h:1025: multiple definition of `sk_refcnt_debug_release'
kernel/sysctl.o:include/net/sock.h:1025: first defined here
make[1]: *** [kernel/built-in.o] Error 1
make: *** [kernel] Error 2

So we decide to make sk_refcnt_debug_release static to eliminate
the error.
Signed-off-by: NYing Xue <ying.xue@windriver.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -1037,7 +1037,7 @@ static inline void sk_refcnt_debug_dec(struct sock *sk)
 	       sk->sk_prot->name, sk, atomic_read(&sk->sk_prot->socks));
 }
 
-inline void sk_refcnt_debug_release(const struct sock *sk)
+static inline void sk_refcnt_debug_release(const struct sock *sk)
 {
 	if (atomic_read(&sk->sk_refcnt) != 1)
 		printk(KERN_DEBUG "Destruction of the %s socket %p delayed, refcnt=%d\n",